Butterfly is the song from Kiloblaster (DOS).
In Episode 1: Death of a Startship, it plays in several levels: 1, 2, 3 (all three pictured) and later repeats in Level 16, 17 and 18.
In Episode 2: No Way Out, it is used again to play in the main menu but no in any more level.
The filenames of the track are SONG_2.KB1 and SONG_8.KB2 (the last digit in the file extensions is the number of the episode using the song). The checksums of each file are the same, meaning they are identical.